The present invention relates to a method of and apparatus for searching a fiducial point of machining in a lathe which has a C-axis control function enabling control of the rotational speed and angle of the spindle during the time of machining.
To date, when an axially asymmetric workpiece having a protuberance or a dent located on its inner or outer circumference or on its end surface and prescribed by the angle defined between this and the fiducial point of machining in the direction toward the C-axis is machined by such a lathe, it is necessary for the fiducial point of machining prescribed in the machining program to be accurately set in relation to the C-axis origin which is assumed to be an criterion of the C-axis control. For this reason, specific jigs and the like have been used in such a lathe.
However, according to this method, various jigs have to be prepared in accordance with each kind of workpiece to be machined. This is inconvenient in the light of the recent tendency to manufacture goods in small amounts and in many variaties. If such jigs are not used, the step of setting up workpieces becomes time-consuming and cannot be carried out with high accuracy. The conventional method is thus disadvantageous.